Sleep homeostasis is a powerful mechanism, which forces us to sleep over and above daily requirements after a sleep loss or sleep deprivation (SD). SD increases homeostatic sleep pressure (HSP), which is manifested as increased sleepiness and impaired cognition, while recovery sleep (RS) reverses these consequences. The investigation of the biochemical changes, triggered in the brain during SD, is one of the key steps towards counteracting the deleterious effects of sleep loss. Extensive research to date has identified the cholinergic basal forebrain (BF) as an important site in sleep homeostasis. Recently, we discovered a biochemical cascade, which is triggered in the BF during SD and promotes RS: it begins with a rapid induction of inducible nitric oxide synthase (iNOS) followed by the increases in NO and extracellular adenosine [AD]ex, first in the BF (1-3h SD) and later in the prefrontal/frontal cortex (PFC/FC) (4-6h SD). The current proposal aims to extend our knowledge on biochemical correlates of sleep homeostasis. We propose that the SD is a qualitatively and quantitatively distinctive state, which is generated by the cross-talk between the BF and PFC/FC nitrinergic, adenosinergic, glutamatergic and cholinergic systems. We see this interaction as central in building up HSP, increase in sleepiness and in impaired performance. We propose following studies to test our hypothesis. Specific Aim 1 (SA1). To investigate whether the increase in extracellular glutamate [Glu]ex is the trigger for iNOS NO AD cascade in the BF and PFC/FC. Our preliminary data (PD) show that the BF [Glu]ex increases within 30min after the beginning of SD, preceding the increases in nitrate/nitrite [NOx-]ex and [AD]ex. Also, we will investigate the consequences of genetically manipulated decrease in BF [Glu]ex. We also show that SD- induced [AD]ex prevents progressive increase in [Glu]ex during SD and thus protects brain from excitotoxic damage. SA2. To investigate whether cholinergic (ChBF) cells are key elements in triggering iNOS->NO->AD cascade in the BF and PFC/FC. Our PD show that iNOS is induced mostly in ChBF cells. Also our PD show that the lesion of ChBF cells using 192 IgG-saporin blocks increase in the BF [NOx-]ex and prevents triggering Glut iNOS NO AD cascade in PFC/FC. We will also identify the cellular source of PFC/FC iNOS/NO using Diaminofluorescein-2 Diacetate and immunohistochemistry. SA3. To investigate whether iNOS NO AD cascade in the PFC/FC contribute towards synaptic plasticity as determined by AMPA receptor (AMPAR) subunit phosphorylation-dependent trafficking. We will infuse iNOS inhibitor or A1R antagonist to the PFC/FC during SD and measure the changes in GluR1 and GluR2 phosphorylation. Our PD show that iNOS blocking reverses SD-induced effects. SA4. To investigate whether chronic SD (CSD) triggers iNOS NO AD cascade in the BF and PFC/FC. Our PD indicate that apart from daily SD-induced increases in [Glut]ex, [NOx-]ex and [AD]ex, the basal levels of [NOx-]ex and [AD]ex increase during 5 days CSD and correlate with the increase in sleepiness. We will investigate whether iNOS or A1R block will affect sleepiness and AMPAR trafficking.